Pull-In Head Assembly

ABSTRACT

A pull-in head assembly (8) for releasably connecting a pulling arrangement (112) to an elongate flexible structure (4, 6). The pull-in head assembly 8 comprises a pull-in head having a body (30) which defines a pulling axis X of the pull-in head. The body (30) has a front end and a rear end and a bore (48) which extends through the body (30) along the pulling axis X. The bore (48) is configured such that a pulling line (28) can be threaded through the body (30).

This invention relates to a pull-in head assembly, apparatus, a methodof installing an elongate flexible structure and particularly, but notexclusively, relates to a pull-in head assembly and installation methodfor a cable protection system.

Cables and other flexible products whether on land, in the dry, or infresh/brackish water or subsea environments have been installed intoinfrastructure for many years using simple, reliable equipment.

Due to the mass of the power cables, which can be 10 kg/m to over 150kg/m, the co-efficient of friction and installation geometries, thewinching cable tension required to deploy or install them from a vesselor barge or trailer may well fluctuate from 1 kN to over 150 kN (15tonnes) depending on the capability of the infrastructure winchingsystem and/or vessel hold back winch/cable engine.

The tension in the winching cable can instantaneously increase (spike)due to high levels of axial stiffness within the cable. An abruptincrease in tension may also occur if any of the fasteners used tosecure a winching cable to the cable (e.g. ferrules, links, stockings,couplings) makes contact, is constrained against (i.e. snags) orgeometrically locks with (including friction effects) any external orinternal abutment.

Any large tension spike can lead to the damage of the relativelyexpensive cable. If the system is being installed subsea, any delay inoperations to investigate causes of snagging and any rectification tofix damaged equipment or assets can lead to costly and time-consumingactivities.

In recent years, it has been recognised that cables are most liable todamage, and a consequent large insurance claim, during the installationphase.

To protect cables during the installation phase, but also throughouttheir service-life, Cable Protection Systems (CPS) have been developed.Cable Protection Systems typically comprise a flexible protective sleevethat extends along the outside of the cable to protect the cable fromdamage during installation and subsequent use. Cable Protection Systemsmay have several functions including preventing the minimum bend radiusof a cable from being compromised, preventing excessive tension beingapplied to a cable and/or protecting a cable from scour once installed.However, by the inclusion of such a system temporarily or permanentlynear or onto the cable end or at a constraining feature located alongthe length of the cable, such as a centraliser—when fitted inside aJ-tube—the installation can become problematic.

Historically, two winching cables (typically known as messenger lines)are used to install a cable and a Cable Protection System. One winchingcable is connected to the cable and the other connected to the CableProtection System.

In this instance, the Cable Protection System and the cable are pulledtogether into a structural interface, which has latches or latchingfeatures, to constrain the Cable Protection System to the supportstructure.

After the Cable Protection System has been confirmed as beingconstrained using the first winching cable, the second winching cable isused to pull the cable up to a hang-off within the support structure.

Both the cable and the Cable Protection System are prone to rotationduring installation, as they are not rotationally constrained andmanufacturing stresses or pre-cable coiling processes, such as windingthe cable into a carousel, can cause torque wind-up, which tends toequalise itself with connected assemblies as the cable is deployed inone continuous length from the vessel and pulled into the foundationunder tension. The winch wire can also induce additional wind-up due toits spiral configuration. Low rotational ropes, with counter spirallayers, attempt to mitigate this issue with minimal torque beingdeveloped under tension.

Winching cables are therefore prone to become entangled with one anotherwhich leads to costly delays or even system removal for a repeat attemptto rectify the predicament.

Furthermore, this can lead to the Cable Protection System beinginstalled at any orientation angle.

Although this does not affect the ability to install the CableProtection System into the Structural interface it does mean that due tothe offset arrangement the required Cable Protection System pull inforce is unpredictable; as it is related, amongst other factors, to theinstallation orientation and departure angles.

In alternative arrangements, a single winching cable may be used whichis connected via a weak link to the Cable Protection System and is alsoconnected to the cable such that, once the Cable Protection System isinstalled, the weak link fails allowing the cable to be subsequentlydrawn into position.

A further problem associated with known installation equipment issnagging of the connectors between the winching cables and the pull-inheads on undersea structures and on the structure itself duringinstallation.

It is an aim of the present invention to at least partly mitigate theabove-mentioned problems.

It is an aim of certain embodiments of the invention to provide animproved pull-in head assembly and/or apparatus for installing a cableand cable protection system.

It is an aim of certain embodiments of the invention to provide animproved pull-in head assembly and/or apparatus that minimises the riskof entanglement and/or snagging during installation of an elongateflexible structure such as a Cable Protection System, a flexible subseapipe or an umbilical.

According to a first aspect of the present invention there is provided apull-in head assembly for releasably connecting a pulling arrangement toan elongate flexible structure, comprising a pull-in head having a bodywhich defines a pulling axis of the pull-in head, the body having afront end and a rear end and a bore which extends through the body alongthe pulling axis, wherein the bore is configured such that a pullingline can be threaded through the body.

The pull-in head assembly may further comprise a flexible pulling linewhich extends through the bore of the body. The pulling line maycomprise a fastener at one end for fastening the pulling line to the endof a cable.

The body may be configured to slide freely along at least the portion ofthe pulling line which extends through the bore.

The pulling line may further comprise a stopper spaced away from thefastener and the body is disposed between the end of the pulling linehaving the fastener and the stopper such that the stopper is engageablewith the body to limit movement of the fastener away from the body alongthe pulling axis.

The pulling line may comprise a connecting feature for connecting thepulling line to a pulling cable. The connecting feature may be disposedat the end of the pulling line which is opposite the end having thefastener. The stopper may be disposed between the connecting feature andthe fastener.

The stopper and the connecting feature may be spaced apart along thepulling line by a distance which is not less than 1 metre. The stopperand the connecting feature may be spaced apart along the pulling line bya distance which is not less than 5 metres. The stopper and theconnecting feature may be spaced apart along the pulling line by adistance which is not less than 10 metres.

The pulling line may comprise a plurality of filaments. The fastener maycomprise a cable grip formed by the plurality of filaments. At least aportion of the stopper may be woven from the plurality of filaments. Theconnecting feature may comprise an eye formed from the plurality offilaments.

A portion of the bore at the front of the body may converge from thefront of the body in the rearward direction. A portion of the bore atthe rear of the body may converge from the rear of the body in theforward direction. The bore may be coaxial with the pulling axis.

According to a second aspect of the invention there is provided anapparatus comprising a pull-in head assembly in accordance with any oneof the preceding claims; and an elongate flexible structure comprisingan elongate flexible element and a connector for connecting the elongateflexible structure to a support structure, wherein the pull-in headassembly is secured to the connector.

The connector may have an internal bore which extends along alongitudinal axis of the connector. At least the rear end of the pull-inhead may be disposed within the bore. The elongate flexible element maybe an elongate tubular element.

The pull-in head assembly may comprise a flexible pulling line whichextends through the bore of the body. The pulling line may comprise afastener at one end for fastening the pulling line to the end of acable. The pulling head assembly may be arranged such that at least aportion of the fastener is disposed within the elongate tubular element.

According to a third aspect of the present invention there is provided amethod of installing an elongate flexible structure comprising thesteps:

providing a pull-in head assembly in accordance with the first aspect ofthe invention;

securing the pull-in head assembly to an elongate flexible structure;and

pulling the pull-in head assembly together with the elongate flexiblestructure into a desired location.

The pull-in head assembly may further comprise a pulling line whichextends through the bore of the body, wherein the pulling line comprisesa fastener at one end for fastening the pulling line to the end of acable, and the elongate flexible structure comprises a flexible tubularelement and a connector for connecting the elongate flexible structureto a support structure, wherein the method further comprises the stepsof

securing the pull-in head assembly to the elongate flexible structuresuch that at least a portion of the fastener is disposed within theflexible tubular element;

securing the fastener to the end of a cable that extends along at leasta portion of the elongate flexible tubular element; and

pulling the cable together with the pull-in head assembly and theelongate flexible structure into a desired location.

In the context of the present invention, a pull-in head (which is alsosometimes referred to as a pulling head) is a device that is used totemporarily couple a pulling arrangement, such as, but not limited to, awinching system, to the end of an elongate flexible structure, such as,but not limited to, an end fitting for a pipe, tube or a cable, so thatthe elongate flexible structure can be pulled (e.g. winched) along asurface, trench, bore or along the side or within a structure, or evenlifted, into a desired position, such as, but not limited to, intoengagement with a connector or fastener provided on a support structure.

A pull-in head typically includes a body portion which, in the case ofpulling heads used to install a tubular elongate flexible structure, canbe inserted into the end of the end of the tubular elongate flexiblestructure and secured using a fastener to the end of the tubularelongate flexible structure.

A common characteristic of pull-in heads is that they are removed froman elongate flexible structure once installation of the elongateflexible structure is complete.

Certain embodiments of the invention provide an improved means forconnecting a pulling arrangement, such as a winching mechanism, to anelongate flexible structure such that the pulling arrangement can beused to pull the elongate flexible structure into a desired position,and to release the pulling arrangement from the elongate flexiblestructure once in the desired position.

Certain embodiments of the invention provide a pull-in head assemblywhich help minimise the risk of snagging on obstacles during use and/orhelps minimise the risk of a geometric lock of fasteners securing apull-in head assembly to a pulling arrangement. For example, certainembodiments of the present invention reduce the risk of snagging onundersea structures when used to install subsea Cable Protection Systemscompared with known arrangements.

It is an aim of certain embodiments of the invention to provide animproved pull-in head assembly and/or apparatus that is easy to assembleand/or easy to secure to an elongate flexible structure.

Certain embodiments of the invention may be used for connection of anelongate flexible structure, such as a Cable Protection System, flexiblesubsea pipe or umbilical, to a marine support structure such as, but notlimited to, a monopile for a wind turbine or a J-tube bellmouth.

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings in which:

FIG. 1 shows some components of an apparatus comprising a pull-in headassembly;

FIG. 2 is a bottom view of a portion of the apparatus shown in FIG. 1;

FIG. 3 is a sectional view along line B-B of FIG. 2;

FIG. 4 is a perspective view of some of the components of the apparatusshown in FIG. 1;

FIG. 5 is a perspective view of the components shown in FIG. 4 from adifferent perspective;

FIG. 6 is a flow chart illustrating steps of an installation process;

FIG. 7A shows a step of an installation process;

FIG. 7B shows a further step of an installation process;

FIG. 7C shows a further step of an installation process;

FIG. 7D shows a further step of an installation process;

FIG. 7E shows a further step of an installation process;

FIG. 8 is sectional view illustrating a transition step of theinstallation process shown in FIGS. 7A to 7E;

FIG. 9 is sectional view illustrating a further transition step of theinstallation process shown in FIGS. 7A to 7E;

FIG. 10 shows illustrates connection between a connector and an elongateflexible sleeve; and

FIG. 11 is a schematic representation of a further apparatus comprisinga pull-in head assembly.

FIGS. 1 to 3 show part of an apparatus 2 comprising a first elongateflexible structure 4, a second elongate flexible structure 6 and apull-in head assembly 8.

The first elongate flexible structure 4 comprises an elongate flexibleelement in the form of a tubular flexible sleeve 10 (shown in part inbroken lines) and a connector 12 for connecting the first elongateflexible structure 4 to a support structure such as a monopile for awind turbine or within a bellmouth of a J-tube. The elongate flexiblesleeve 10 is secured to the connector 12 by a geometric interlockingarrangement between an end of the elongate flexible sleeve 10 and agroove 12 a provided at one end of the connector, as illustrated in FIG.10. Alternatively, or in addition, the sleeve 10 may be secured to theconnector 12 by bonding, clamping and/or other suitable means. In theembodiment shown, the connector 12 is a type of connector which iscommonly referred to as an end fitting. The elongate flexible sleeve 10and the connector 12 form a Cable Protection System (CPS) which istypically used during the installation of subsea power cables in orderto protect a cable within the sleeve 10 from damage during theinstallation process and subsequent operation.

The connector 12 comprises a hollow cylindrical connector body 14 havingfirst and second halves 14 a, 14 b (only the first half 14 a is shown inFIG. 1) which, when assembled, are held together by straps 16 a, 16 b,16 c located in respective circumferentially extending external grooves18 a, 18 b, 18 c in the connector body 14.

A cylindrical bore 19 extends along the longitudinal axis of theconnector body 14. The bore provides an inner surface 20 of theconnector body 14. The inner surface 20 has a recess in the form of afirst annular groove 22 extending around the longitudinal axis of theconnector body 14. The first annular groove 22 has a V-shaped crosssection when viewed in the circumferential direction. The annular groove22 has a front surface 22 a which is inclined from the apex of thegroove 22 in a direction which is radially inward and forward withrespect to the longitudinal axis of the connector body 14. The annulargroove 22 has a rear surface 22 b which is inclined from the apex of thegroove 22 in a direction which is radially inward and rearward withrespect to the longitudinal axis of the connector body 14. The connectorbody 14 has a conical front portion 23 which tapers in the forwarddirection along the longitudinal axis of the connector body 14. Thefront portion 23 has a conical abutment surface 23 a which is configuredto engage with a connector mounted on a subsea structure, as describedwith reference to FIGS. 8 and 9 below.

The second elongate flexible structure 6 comprises a cable 24 such as asubsea power cable. Typically, subsea power cables are used to transferpower from an offshore electrical power generator such as a wind turbineto a base station or to provide interconnection between wind turbinesforming part of an array of wind turbines. A subsea power cabletypically comprises several conductors, each of which is surrounded aconductor screen. The conductors are bundled together with fillers andcommunication cables, where appropriate, and the bundle is surrounded byone or more layers of armour (typically steel armour wires), tape orbituminous compound which provide protection. A subsea power cabletypically has an overall diameter of between 50 mm and 300 mm.

The pull-in head assembly 8 comprises a pull-in head 26 and a pullingline 28.

With reference to FIGS. 3 to 5, the pull-in head 26 comprises a body 30,a retaining member 32 and a securing plate 34. The body 30 has a frontportion 36, a middle portion 38 and a rear portion 40. The body 30 has alongitudinal axis which defines a pulling axis X of the pull-in head 26.The front portion 36 has a conical outer profile which tapers in theforward direction along the pulling axis. The diameter of the frontportion 36 is slightly greater than the diameter of the portion of theconical front portion 23 against which it abuts such that the frontportion 36 overhangs slightly—which reduces the risk of snagging of theconical front portion 23 during installation. The middle portion 38 hasa cylindrical profile. The diameter of the front portion 36 at theinterface with the middle portion 38 is larger than the diameter of themiddle portion 38 such that the front portion 36 defines a first annularabutment face 42 which abuts against the connector body 14, as shown inFIG. 3. The rear portion 40 also has a cylindrical profile. The diameterof the rear portion 40 is smaller than the diameter of the middleportion 38 such that middle portion 38 defines a second annular abutmentface 44 against which the retaining member 32 located. The rear portion40 has a recess in the form of a second annular groove 46 extendingaround the pulling axis X.

A bore 48 extends along the whole length of the body 30. The bore 48 iscoaxial with the pulling axis X and defines an opening at each end ofthe bore 48. The bore 48 has divergent portions 50, 52 and the front andrear of the bore 48 respectively which are configured to reduce thelikelihood of binding with the pulling line 28, as explained later.

The retaining member 32 is annular and extends circumferentially aroundthe pulling axis X. The retaining member 32 comprises an innercylindrical portion 54, through which the rear portion 40 of the body 30extends, and an outer conical portion 56. In the present embodiment, theinner cylindrical portion 54 and the outer conical portion 56 are formedfrom a single piece of resilient material such as a polymeric material,for example rubber and/or polyurethane having a shore hardness betweenShore 60A and Shore 60D. The outer conical portion 56 comprises sixindividual retaining elements 58, in the form of fingers, which arearranged circumferentially around the pulling axis X. Each retainingelement 58 extends radially outwardly from the inner cylindrical portion54 with respect to the pulling axis X and rearwardly with respect to thebody 30. In the present embodiment, each retaining element 58 extends atan angle of 30 degrees with respect to the pulling axis X. In otherembodiments, the angle can be set according to requirements but ispreferred to be between 20 degrees and 70 degrees, such as not less than30 degrees and not more than 50 degrees, in order to provide reliablerelease under a predetermined loading, as described later. Theindividual retaining elements 58 are shown most clearly in FIGS. 4 and5. Each element 58 has an outer surface 60 which is curved to match theprofile of the front surface 22 a of the groove 22 against which itabuts. Consequently, the retaining member 32 is free to rotate withinthe groove 22 with respect to the connector body 14. Each element 58 isconfigured such that it flexes and compresses radially inwardly towardsthe pulling axis X when the pull-in head 26 is pressed with sufficientforce against the front surface 22 a of the connector body 14.

The retaining member 32 is held in abutting engagement with the secondabutment face 44 by the securing plate 34. The securing plate 34comprises a circular disc which is fastened to the rear of the body 30by bolts 62 (see FIG. 5) or other suitable fastening means. The securingplate 34 has a central aperture 35 which is aligned with the bore 48.

The pulling line 28 comprises a connecting loop 64 at one end forconnecting the pull-in head assembly 8 to a winching cable or otherpulling arrangement, a fastener 66 at the other end for fastening thepull-in head assembly 8 to the cable 24, and a stopper 68 which isdisposed between the connecting loop 64 and the fastener 66.

In the embodiment shown, the pulling line 28 is woven from filamentsmade of a soft flexible material having a high tensile strength such asKevlar™. The pulling line 28 may comprise, as an alternative or inaddition, galvanised or stainless steel. The fastener 66 comprises ameshed tubular element which fits over the end of the cable 24. Thefastener 66 is configured to form a cable grip into which an end of thecable 24 can be inserted. The filaments which form the fastener portionof the pulling line 28 are woven in a configuration in which thefastener 66 contracts around the cable 24 when a tension is applied tothe pulling line. The arrangement is known in the art of cableinstallation as a pulling stocking, a cable grip, a cable stocking or aChinese finger.

The portion of the fastener 66 which is not used to grip the cable 24extends through the bore 48 which itself extends along the body 30 ofthe pull-in head 26 and the central aperture 35 of the securing plate34. The stopper 68 is formed by weaving the filaments into a bulbousformation which has a maximum width that is greater than the opening atthe front end of the bore 48. The stopper 68 may be formed by weavingthe filaments around a rigid structure such as a bead or bobbin-likeelement.

The connecting loop 64 is formed by a fold of the filaments back onthemselves and weaving the ends of the filaments together in the portionof the pulling line 28 between the connecting loop 64 and the end of thefastener 66. In the embodiment shown, the connecting loop 64 is adjacentthe stopper 68. In alternative embodiments, the connecting loop 64 maybe spaced away from the stopper 68 by up to 1 m or up to 5 m or up to 10m or more.

In order to assemble the apparatus, the pull-in head assembly 8 may befirst assembled by threading the end of the pulling line 28 having thefastener 66 through the bore 48 of the body 30 of the pull-in head 26such that the fastener 66 extends from the rear of the pull-in head 26and the connecting loop 64 and the stopper 68 are at the front of thepull-in head 26.

An end of the cable 24 is then inserted into the fastener 66. During theinsertion, no tension is applied to the pulling line 28 so that the endof the cable 24 can slide easily into the fastener 66. The fastener 66may even be compressed slightly in the longitudinal direction in orderto expand the fastener 66 in order to receive the end of the cable 24more easily. Once inserted, the fastener 66 can be released or a slighttension applied in order to contract the fastener 66 around the end ofthe cable 24 to grip the cable 24.

In this configuration, the pull-in head 26 is retained on the pullingline 28 by the stopper 68 and the cable 24/fastener 66.

Once the pull-in head assembly 8 has been secured to the cable 24 asdescribed above, the body 30 of the pull-in head 26 is placed within thefirst half 14 a of the connector body 14 such that the outer conicalportion 56 of the retaining member 32 is located within the firstannular groove 22 formed on the inner surface 19 of the connector body14, as shown in FIG. 1. The pulling axis X is coaxial with thelongitudinal axis of the connector 12. The second half 14 b of theconnector body 14 is then placed over the first half 14 a and the twohalves 14 a, 14 b are clamped together by the straps 16 a, 16 b, 16 c.

Once assembled, the pull-in head 26 is prevented from moving axiallyalong the pulling axis with respect to the connector 12 by the firstannular abutment face 42, which abuts against the front of the connector12, and the retaining member 32. When a pulling force is applied alongthe pulling line 28, the cable 24 is drawn forward into abuttingengagement with the securing plate 34 (it will be appreciated that aportion of the fastener 66 will be sandwiched between the end of thecable 24 and the securing plate 34, but is prevented from bindingagainst the body 30 by the divergent portion 52 of the bore 48). Theforce exerted by the cable 24 on the securing plate 34 is transmittedthrough the retaining member 32 to the connector body 14. Consequently,the connector 12 and the sleeve 10 forming the Cable Protection Systemare drawn along with the pull-in head 26 when the pull-in head is pulledin a direction along the pulling axis X. The pull-in head 26 is,however, rotatable about the pulling axis X with respect to theconnector 12.

As explained above, the retaining member 32 is formed from a singlepiece of resiliently deformable material. The retaining elements 58 willtherefore deflect radially inwardly when the retaining elements 58 arepressed against the front surface 22 a of the groove 22 in the connectorbody 14 with sufficient force. The retaining member 32 is configuredsuch that retaining elements 58 will deform radially inwardly by anamount which allows the pull-in head 26 to be pulled out of the end ofthe connector 12 only when a pulling force exceeding a predeterminedthreshold is applied. The predetermined threshold is determined based onthe desired application for the pull-in head assembly 8. The retainingmember 32 can be configured to release at a predetermined pulling forcealong the pulling axis X (defined as a release force of the pull-in headassembly 8) by selecting the number and/or thickness of the retainingelements, material type, material thickness, length of the retainingelements. For example, the release force may be set by selection of asuitable number of retaining elements. The release force may also be setby selection of a suitable thickness of one or more of the retainingelements. The release force may also be set by selection of a suitableangle at which the or each, or at least one, retaining element extends.For example, the actual angle will be dependent on the specificapplication and may be set based on one or more factors including cablediameter, Cable Protection System outer diameter, expected tension inthe cable/winching cable during installation, desired release force (andcorresponding tension in the cable/winching cable) and stiffness of theapparatus. The factors used to set the release force may be determinedby onshore testing prior to offshore installation.

The release force may also be set by varying the coefficient of frictionbetween the contact faces of the retaining member 32 and the frontsurface 22 a of the groove 22 of the connector body 14. The coefficientof friction may be varied by providing a specific surface finish on oneor both surfaces and/or by application of a lubricant between thesurfaces. The type of fit between the retaining member 32 and theconnector body 14 can be selected in accordance with a desired releaseforce. The type of fit may be one of a clearance fit, an interferencefit and a transition fit. In addition, a material of the retainingmember can be selected having a desired bulk modulus.

Once assembled as described above, the apparatus 2 is ready forconnection to a winching cable.

FIG. 6 is a flow chart illustrating a method of connecting the apparatus2 to a monopile for a wind turbine.

FIG. 7A is a schematic representation of an apparatus 2 at step 1002during installation.

The monopile 102 is located on the sea bed 104. The monopile 102comprises a tubular body 105 which extends vertically and has a circularaperture 106 near to the base of the monopile 102 for receiving a powercable into the monopile 102. The aperture 106 is located in a region ofthe monopile 102 which is submerged when the monopile 102 is located onthe sea bed 104. A monopile connector 108 is provided at the aperture106 for connecting to a Cable Protection System as described below. Themonopile 102 has a hang-off point 110 within the monopile 102 to which acable arrangement can be connected.

Prior to installation, a winching cable 112 (typically known in the artas a messenger line) is threaded downwardly through the body 105 of themonopile from a winch (not shown) past (or through) the hang-off point110 and through the aperture 106 out of the monopile 102. The end of thewinching cable 112 is provided with a fastener 114 such as a clasp whichis connected to the connecting loop 64 of the pull-in head assembly 8.

Initially, the apparatus 2, which comprises the sleeve 10 and connector12, the cable 24 and the pull-in head assembly 8 as described above, maybe spooled on a vessel such as a boat.

Once the winching cable 112 has been secured to the connecting the loop64, the winch is activated to pull the pull-in head assembly 8 from thetransport vessel downwardly towards the base of the monopile 102. As thepull-in head assembly 8 travels downwardly, the connector 12 is pulleddownwards with the pull-in head assembly 8, as shown in FIG. 7A, suchthat the sleeve 10 and the cable 24 unspool from the transport vessel.

As the pull-in head assembly 8 travels downwardly, the weight of thesleeve 10, cable 24, connector 12 and the pull-in head 26 (which is freeto slide along the portion of the pulling line 28 between the stopper 68and the end of the cable 24) causes the connector 12 to push downagainst the stopper 68. The stopper 68 therefore prevents the pull-inhead 26 and the connector 12 from sliding downwardly away from the endof the cable 24.

As the sleeve 10 unspools, a torque is generated by the sleeve 10 aboutthe longitudinal axis of the sleeve 10 and hence the pulling axis X. Thetorque is a consequence of the residual stresses within the sleeve 10that are introduced during manufacture or by the winding of the sleeve10 onto the spool. This torque is transferred to the connector 12. Sincethe connector 12 is free to rotate with respect to the pull-in head 26(as described above), the pull-in head assembly 8 significantly reduces,and may eliminate entirely, the transfer of torque from the sleeve 10 tothe winching cable 112. It will be appreciated that the pull-in head 26is also free to rotate with respect to the pulling line 28, which canalso help to alleviate torque transfer.

In the embodiment shown in FIG. 7A, the distance between connecting loop64 and the stopper 68 is 1 m (the arrangement is therefore different inthis respect from the embodiment shown in FIGS. 1 to 5 in which theconnecting loop 64 is shown adjacent the stopper 68). The distancebetween the connecting loop 64 and the stopper 68 ensures that thefastener 114 and the connecting loop 64 are drawn through the aperture106 while the pull-in head assembly 8 is travelling downwardly. In thisorientation, the weight of the apparatus 2 is against the stopper 68 (orelse is supported by the surrounding water) and so the tension acting onthe winching cable 112 is relatively low. Consequently, the risk ofsnagging of the fastener 114 and/or the connecting loop 64 as they passthrough the aperture 106 is minimised. The divergent portion 50 of thebore 48 accommodates the stopper 68 and helps prevent binding of thestopper 68 against the body 30.

FIG. 7B shows installation of the apparatus 2 at step 1004 as thepull-in head assembly 8 draws level with the aperture 106. At step 1004,the fastener 114 and the connecting loop 64 have passed through theaperture 106 following which the risk of snagging is reduced.

FIG. 7C shows installation of the apparatus 2 at step 1006 as thepull-in head assembly 8 is adjacent the aperture 106. At step 1006, thefront portion 36 of the body 30 slides through the aperture 106 whilethe pull-in head assembly 8 is horizontal. The conical outer profile ofthe front portion 36 of the body 30 and the conical abutment surface 23a of the connector body 14 allow the pull-in head 26 and the connector12 to slide over the edge of the aperture 106 which minimises the riskof snagging as the apparatus 2 is drawn through the aperture 106.Furthermore, the weight of the apparatus 2 still does not contributesignificantly to the tension on the winching cable 122. The risk ofsnagging therefore remains low.

FIG. 7D shows installation of the apparatus 2 at step 1008 as theconnector 12 is brought into engagement with the monopile connector 108.The transition from step 1008 to step 1010, shown in FIG. 7E, in whichthe pull-in head 26 has been separated from the connector 12 will bedescribed with reference to FIGS. 8 and 9.

FIG. 8 shows the monopile connector 108 having an aperture 116 throughwhich the pull-in head assembly 8 is drawn by the winching cable 112.

An annular abutment surface 118 surrounds the aperture 116. The annularabutment surface 118 is arranged to receive the front portion 23 of theconnector body 14. In order to ensure that the connector 12 is correctlyaligned with the monopile connector 108, the annular abutment surface118 is conical and has a profile that corresponds to the profile of theconical abutment surface 23 a of the front portion 36 of the connectorbody 14. Thus, as the front portion 36 of the pull-in head 26 is drawnthrough the aperture 116, the conical abutment surface 23 a of theconnector body 14 and the annular abutment surface 118 of the monopileconnector 108 are brought into contact and slide over each other toalign the connector 12 with the monopile connector 108. Once theconnector 12 has been engaged completely with the monopile connector 108(in this instance, complete engagement is when the connector 12 and themonopile connector 108 are coaxially aligned and the conical abutmentsurface 23 a and the annular abutment surface 118 are contiguous, asshown in FIG. 8) a latching mechanism (not shown) is used to secure theconnector 12 into engagement with the monopile connector 108. Thelatching mechanism may be manual or automatic.

Throughout steps 1002 to 1008, the pulling force exerted on the pull-inhead 26 along the pulling axis X is not expected to exceed apredetermined threshold. For example, the drag force, friction force andother forces (which are invariably present when pulling a cable and aCable Protection System from a spool) can be expected, in the absence ofsnagging events, to be below a threshold force. The threshold force willbe dependent on many factors including, but not limited to, the lengthof the cable unspooled, the length of the Cable Protection Systemunspooled, the dimensions (such as a cable diameter or a width) of thecable and the Cable Protection System, the force required to trigger alatching mechanism of the monopile connector (or other connector) andother factors. Nevertheless, a threshold force that can be expected tobe not exceeded during an installation process can be determined, forexample, using empirical data or modelling.

In the present embodiment, the force exerted on the pull-in head 26along the pulling axis X is not expected to exceed 60 kN throughoutsteps 1002 to 1008.

Once the connector 12 has engaged with the monopile connector 108completely, the monopile connector 108 prevents further advancement ofthe connector 108. Consequently, an increase in the pulling forceexerted by the winch along the winching cable 112 translates into anincrease in the force exerted on the pull-in head 26 along the pullingaxis X. When the pulling force exerted on the pull-in head 26 along thepulling axis X exceeds a predetermined amount, which is set at or abovethe threshold force, for example at a force between 15 kN and 150 kN,for example at a force between 80 kN and 120 kN, such as 100 kN for theembodiment shown, the force exerted by the front surface 22 a of thegroove 22 in the connector body 14 on the individual retaining elements58 cause the retaining elements 58 to deflect radially inwardly and/orcompress, allowing the pull-in head 26 to move out of the connector 12,as shown in FIG. 9. Deflection of the retaining elements 58 inwardly isaided by deflection of the inner cylindrical portion 54 into the secondannular groove 46. It will also be appreciated that the spacing betweenadjacent retaining elements 58 allows the retaining elements to collapseinto the voids between the adjacent retaining elements 58 withoutobstructing each other.

It will be appreciated that variation in manufacturing tolerances,temperature, environmental factors and other factors may contribute tofluctuations in the actual pulling force that is required to release thepulling head assembly. Such factors may be taken into consideration byconfiguring the pulling head assembly such that the release force willnot fluctuate outside a predetermined range. For example, the releaseforce will not fall below 80 kN under normal operation and will notexceed 120 kN during normal operation. The term predetermined releaseforce should therefore be understood as a release force which could beexpected under predetermined conditions.

As the retaining member 32 moves from the groove 22 through the end ofthe connector 12, the retaining elements 58 are compressed, as describedabove, into a release configuration in which the outer surfaces 60 ofthe respective retaining elements 58 define a substantially cylindricalouter profile having a diameter which corresponds to the internaldiameter of the bore 19 through the connector body 14. The pull-in head26 can therefore be separated from the connector 12 along the pullingaxis X and pulled upwardly through the monopile 102 in accordance withstep 1010 as shown in FIG. 7E.

The retaining member 32 provides a mechanical fuse which causes thepull-in head assembly 8 to release from the connector 12 when a pullingforce along the pulling axis X exceeds a predetermined threshold. Thisensures that release of the pull-in head assembly 8 is predictable andreliable and occurs only when the connector 12 has been connected to themonopile connector 108. Furthermore, the arrangement on the retainingelements 58 about the pulling axis X ensures that a pulling forceexerted along the pulling axis X which is transmitted from the pullinghead to the connector 12 is distributed around the pulling axis X.Consequently, force required to release the pull-in head assembly 8 fromthe connector 8 is independent of the orientation of the pull-in head 26with respect to the connector 12 and the orientation of the connector 12with respect to the monopile connector 108 with which it engages.

Once the pull-in head 26 has separated from the connector 12, the end ofthe cable 24 which remains attached to the pull-in head 26 slides outfrom the sleeve 10 and the connector 12 and is pulled with the pull-inhead 26 to the hang-off point 110 within the monopile 102.

It will be appreciated that once the pull-in head 26 has transferredfrom the configuration shown in FIG. 8 to the configuration shown inFIG. 9, the pulling force exerted along the pulling axis X may reducesince the retaining member 32 has escaped the groove 22 and may furtherreduced as the pull-in head 26 exits the connector 12. Consequently, thetransition from the configuration shown in FIG. 8 to the configurationshown in FIG. 9 may be identified by a spike in the pulling forceapplied to the pull-in head 26.

Although in the embodiment described above the retaining member isformed as an integrated component comprising a single piece of material,it will be appreciated that the inner cylindrical portion and the outerconical portion may be separate components. The retaining elements mayalso be separate components from each other. The retaining member andthe body of the pulling head may be separate components, as shown in thedescribed embodiments, but may be a single integrated component. Theretaining member and the body may be made of the same or differentmaterials.

An alternative embodiment may comprise a connector having at least twoannular grooves provided in the inner surface defining the bore of theconnector, wherein the grooves are arranged adjacent each other orspaced apart along the longitudinal axis of the connector. Such anarrangement is particularly suitable for applications in which radialspace is restricted, for example, arrangements in which the diameter ofa cable is large relative to the diameter of the cable protectionsystem.

A further embodiment may comprise a rigid retaining member which engageswith a resilient portion of the connector, wherein the resilient portionof the connector is configured to deform in order to release the pullinghead assembly.

In the embodiment shown, the monopile connector has an annular abutmentsurface into which the connector is brought into engagement. It will,however, be appreciated that other means for limiting motion of theconnector could be utilised. For example, the connector could beprovided with an abutment feature, such as a shoulder, at its outersurface which contacts an outer surface of the monopile, or othersupport structure, surrounding the aperture in order to limit furtherforward motion.

Further embodiments may comprise a retaining member which is configuredto break or plastically deform when the pulling force exerted along thepulling axis exceeds a predetermined threshold.

FIG. 11 shows a variation of the apparatus shown in FIG. 1 in which apull-in head assembly 108 comprises a body 130 and a retaining member132 in the form of an annular collar 133 which extends about the pullingaxis X. The annular collar 133 is arranged to engage both the body 130and a connector 112 of a tubular elongate flexible structure 104 suchthat the pull-in head assembly 108 is secured to the connector 112 inthe direction of the pulling axis X. In particular, the annular collar133 is located in respective opposing grooves provided in the body 130and an inner surface of a central bore 119 that extends along theconnector 112.

A mid portion 133 a of the annular collar 133 which extendscircumferentially between the inner radial periphery and the outerradial periphery of the annular collar 133 is configured to yield and/orfracture when a pulling force exceeding a predetermined threshold isexerted on the pull-in head assembly 108 along the pulling axis. Forexample, the mid portion 133 a may comprise a frangible portion whichfractures under a shear stress when a force exceeding a predeterminedthreshold is exerted parallel to the pulling axis X. The mid portion 133a is aligned radially with an interface of an outer surface of the body130 and an inner surface of the bore 133 a. The mid portion 133 adivides the annular collar 133 into an inner portion 133 b and an outerportion 133 c.

During use, when the connector 112 is installed (using a methodcorresponding to the method described previously) and the pulling forceexerted along the pulling axis X exceeds the predetermined threshold,the annular collar 133 breaks along the mid portion 133 a. The innerportion 133 b is then drawn with the body 130 from the connector 112 asthe pull-in head is separated from the connector 112. The outer portion133 c remains within the connector 112 or else is removed separately.

In an alternative embodiment, the annular collar 133 may comprise aplurality of fingers (similar to the retaining elements of theembodiment shown in FIGS. 4 and 5) which shear off when the pullingforce exceeds a predetermined threshold. The fingers may be arranged toextend rearwardly at an angle of between 70 degrees and 90 degrees withrespect to the pulling axis.

In the drawings like reference numerals refer to like parts.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of them mean “including but notlimited to” and they are not intended to (and do not) exclude othermoieties, additives, components, integers or steps. Throughout thedescription and claims of this specification, the singular encompassesthe plural unless the context otherwise requires. In particular, wherethe indefinite article is used, the specification is to be understood ascontemplating plurality as well as singularity, unless the contextrequires otherwise.

Features, integers, characteristics or groups described in conjunctionwith a particular aspect, embodiment or example of the invention are tobe understood to be applicable to any other aspect, embodiment orexample described herein unless incompatible therewith. All of thefeatures disclosed in this specification (including any accompanyingclaims, abstract and drawings), and/or all of the steps of any method orprocess so disclosed, may be combined in any combination, exceptcombinations where at least some of the features and/or steps aremutually exclusive. The invention is not restricted to any details ofany foregoing embodiments. The invention extends to any novel one, ornovel combination, of the features disclosed in this specification(including any accompanying claims, abstract and drawings), or to anynovel one, or any novel combination, of the steps of any method orprocess so disclosed.

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

1. A pull-in head assembly for releasably connecting a pullingarrangement to an elongate flexible structure, comprising: a pull-inhead having a body which defines a pulling axis of the pull-in head, thebody having a front end and a rear end and a bore which extends throughthe body along the pulling axis, wherein the bore is configured suchthat a pulling line can be threaded through the body.
 2. The pull-inhead assembly of claim 1, further comprising a flexible pulling linewhich extends through the bore of the body, wherein the pulling linecomprises a fastener at one end for fastening the pulling line to theend of a cable.
 3. The pull-in head assembly of claim 2, wherein thebody is configured to slide freely along at least the portion of thepulling line which extends through the bore.
 4. The pull-in headassembly of claim 2, wherein the pulling line further comprises astopper spaced away from the fastener and the body is disposed betweenthe end of the pulling line having the fastener and the stopper suchthat the stopper is engageable with the body to limit movement of thefastener away from the body along the pulling axis.
 5. The pull-in headassembly of claim 2, wherein the pulling line comprises a connectingfeature for connecting the pulling line to a pulling cable, theconnecting feature is disposed at the end of the pulling line which isopposite the end having the fastener.
 6. The pull-in head assembly ofclaim 4, wherein the pulling line comprises a connecting feature forconnecting the pulling line to a pulling cable, the connecting featureis disposed at the end of the pulling line which is opposite the endhaving the fastener, and wherein the stopper is disposed between theconnecting feature and the fastener.
 7. The pull-in head of claim 6,wherein the stopper and the connecting feature are spaced apart alongthe pulling line by a distance which is not less than 1 metre, forexample not less than 5 metres, such as not less than 10 metres.
 8. Thepull-in head assembly of claim 2, wherein the pulling line comprises aplurality of filaments.
 9. The pull-in head assembly of claim 8, whereinthe fastener comprises a cable grip formed by the plurality offilaments.
 10. The pull-in head assembly of claim 8, wherein the pullingline further comprises a stopper spaced away from the fastener and thebody is disposed between the end of the pulling line having the fastenerand the stopper such that the stopper is engageable with the body tolimit movement of the fastener away from the body along the pullingaxis, and wherein at least a portion of the stopper is woven from theplurality of filaments.
 11. The pull-in head assembly of claim 8,wherein the pulling line comprises a connecting feature for connectingthe pulling line to a pulling cable, the connecting feature is disposedat the end of the pulling line which is opposite the end having thefastener, and wherein the connecting feature comprises an eye formedfrom the plurality of filaments.
 12. The pull-in head assembly of claim1, wherein a portion of the bore at the front of the body converges fromthe front of the body in the rearward direction.
 13. The pull-in headassembly of claim 1, wherein a portion of the bore at the rear of thebody converges from the rear of the body in the forward direction. 14.The pull-in head assembly of claim 1, wherein the bore is coaxial withthe pulling axis.
 15. Apparatus comprising: the pull-in head assembly inaccordance with claim 1; and an elongate flexible structure comprisingan elongate flexible element and a connector for connecting the elongateflexible structure to a support structure, wherein the pull-in headassembly is secured to the connector.
 16. The apparatus of claim 15,wherein the connector has an internal bore which extends along alongitudinal axis of the connector and at least the rear end of thepull-in head is disposed within the bore.
 17. The apparatus of claim 15,wherein the elongate flexible element is an elongate tubular element.18. The apparatus of claim 17, wherein the pull-in head assemblycomprises a flexible pulling line which extends through the bore of thebody, wherein the pulling line comprises a fastener at one end forfastening the pulling line to the end of a cable, the pulling headassembly is arranged such that at least a portion of the fastener isdisposed within the elongate tubular element.
 19. A method of installingan elongate flexible structure comprising the steps: providing thepull-in head assembly in accordance with claim 1; securing the pull-inhead assembly to an elongate flexible structure; and pulling the pull-inhead assembly together with the elongate flexible structure into adesired location.
 20. The method of claim 19, wherein the pull-in headassembly further comprises: a pulling line which extends through thebore of the body, wherein the pulling line comprises a fastener at oneend for fastening the pulling line to the end of a cable; and theelongate flexible structure comprises a flexible tubular element and aconnector for connecting the elongate flexible structure to a supportstructure, wherein the method further comprises the steps of securingthe pull-in head assembly to the elongate flexible structure such thatat least a portion of the fastener is disposed within the flexibletubular element; securing the fastener to the end of a cable thatextends along at least a portion of the elongate flexible tubularelement; and pulling the cable together with the pull-in head assemblyand the elongate flexible structure into a desired location.